The 3-GPP Evolved Universal Terrestrial Radio Access (E-UTRA) Rel. 10 LTE standard requires the support of at least 300 active non-DRX users in a 5 MHz bandwidth. This is at least a 50% increase over the Rel. 8 standard. Rel. 10 also supports uplink multiple input, multiple output (UL-MIMO) transmission. The increase in supported users and the introduction of multiple transmit antennas per user results in a need for more efficient sounding resource management if the sounding reference signal (SRS) capacity is not increased within the Rel. 10 time frame. Aperiodic sounding reference signal (SRS) transmission was adopted to efficiently manage sounding opportunities across single- and multi-antenna user equipment (UE).
The current adopted features of aperiodic SRS transmission with respect to signaling, resource allocation and transmission timing include:
A UE may be independently configured for periodic and aperiodic SRS transmission;
An exemplary scenario employs periodic sounding for timing control, power control and frequency dependent scheduling for single antenna port transmission and employs aperiodic sounding to enable frequency dependent scheduling for UL spatial multiplexing;
A similar but different set of UE specific parameters as in Rel. 8 periodic sounding is independently configured for aperiodic sounding;
Aperiodic SRS transmission is configured by radio resource control (RRC) signaling and dynamic (L1) signaling in a DCI format;
Rel. 8/9 (time/frequency/code) SRS resources are re-used for aperiodic sounding;
Cell-specific SRS configuration parameters are applicable to both periodic and aperiodic sounding;
Aperiodic sounding using Rel. 8 SRS resources is transmitted in cell-specific SRS subframes;
SRS is transmitted from all configured antenna ports in the same Single Carrier Frequency Division Multiple Access (SC-FDMA) symbol; and
The SRS transmission bandwidth and starting resource block assignment are the same for all antenna ports.
Outstanding or undecided aspects of this process addressed in this invention include:
The number of states needed in the downlink control information (DCI) format conveyed on the Physical Downlink Control CHannel (PDCCH) for triggering/configuration of aperiodic SRS transmission;
The potential list of configuration parameters such as cyclic shift (CS), transmission comb, bandwidth (BW) position, transmission BW and hopping;
The partitioning of configuration parameters between RRC signaling and dynamic signaling in the PDCCH; and
The transmission timing rules for aperiodic SRS transmission.